Rotor wheel for centrifugal pumps



Sept. 4, 1951 E. 56mm 2,566,795

ROTOR WHEEL FOR CENTRIFUGAL PUMPS Filed Dec. 18, 1.5M?

Q nvhmmBRRRa awstsa 88$ Patented Sept. 4, 1951 UNITED STATES PATENTOFFICE ROTOR WHEEL FOR CENTRIFUGAL PUMPS Emile Egger, Cressier,Switzerland Application December 18, 1947, Serial No. 792,553 InSwitzerland December 20, 1946 6 Claims. 1

This invention relates to centrifugal pumps and particularly to rotorwheels thereof serving for the delivery of liquids which contain air orwhich froth or evaporate easily; for the delivery of thick substances oflow to high concentration, substances with admixtures of fibrous, pastyand lumpy solid substances, as well as for the delivery of water with ahigh degree of efliciency.

The basic idea of the invention consists in choosing the sections of theblade passages of the rotor wheel so that the substance to be deliveredmoves away from the concave side of the blades so that a vacuum zone iscreated in the blade passages under the action of the fiow of thesubstance so that the rotor wheel is rendered insensitive to airthereby.

In the accompanying drawings Figs. 1 and 2 are diagrammatic verticalsections at right angles to one another of a constructional example of apump rotor with three blades which iogether with two sets of curves inFigs. 3 and 4 will enable the invention to be understood.

Fig. 5 is a view similar to Fig. 1 of an open two-bladed rotor wheel.

Fig. 6 shows an arrangement particularly for dealin with liquids whichfroth freely.

Fig. 7 illustrates an embodiment with guide vanes in front of theentrance to the rotor wheel.

In Figs. 1 and 2, the width In of the outlet from the rotor wheel is solarge that the passage between two blades I has the effect of anejector, so that, as above-mentioned, in consequence of the flow of theliquid and the action of centrifugal force an increased vacuum iscreated in the blade passage.

The .form of the three blades I of the wheel depends not only on purehydraulic considerations but has to be adapted to correspond to thematerial to be delivered. An object of the form given to the blades I isto produce a moving away of the stream of material to be delivered fromthe concave side of the blades.

The way in which the invention works explained with reference to Figs. 1and 2 and also the curve Fig. 3 is as follows:

The rotor wheel requires first and foremost low liquid velocities, onlythe relative velocities in the rotor wheel itself being a determinedfactor. The velocity of entry at the entrance to the wheel must, ifpossible, not exceed 2 metres per second and have the same value as thevelocities in the suction conduct. A great cross sectional area of theentrance 2 to the wheel results from this requirement.

figure for the velocities are only given by way of example and may, ofcourse. vary within certain limits.

Under the action of the pressure of the atmosphere the liquid will beaccelerated to the absolute velocity Us in the suction pipecorresponding to the vacuum produced in the pump. This imparted absolutevelocity must be kept constant up to the entrance 2 to the rotor wheel,that is to say 17s=Ue. By slightly constricting the cross sectionalareas in the rotor wheel up to the entrance edge 3 of the blade I aslight acceleration to the relative velocity Uer of the material to be Atypical curve of the distribution of the rela delivered at this edge 3is obtained.

By the enlargement of the outlet width bl of the rotor blade to suit thematerial to be delivered and the amplification of the cross sectionalarea of the blade passage aimed! at thereby, the relative liquidvelocity var at the outlet 4 is very greatly reduced. The curve in Fig.3 between De and var shows a smooth sinusoidal course for the relativevelocities in the rotor wheel. This smooth shape is of great importancefor the results obtained.

The ratio of the cross sectional area of the entrance 3 of the bladepassage to the cross sectional area of the outlet 4 of the blade passagemay rise from 1:10, the basic principle involved being that the greaterthe amount of air contained in a medium to be delivered is, or the moreconcentrated a thick substance to be delivered is, the greater the ratiochosen. must be.

By a reduction in the number of blades and/or by suitably shaping theblades I of the wheel the ratio can be very greatly varied (e. g. downto 1:05).

The rotor wheel shown in Figs. 1 and 2, while constructed in accordancewith existing hydraulic principles, was given the form with the width ofoutlet b shown by the dotted lines and had to be provided with fromseven to nine wheel blades.

One of the objects of the invention consists in the abovementionedattainment of a low relative outlet speed as a function of the greatlyincreased cross sectional area of the outlet 4 from the rotor wheel.

If it be supposed that the surface E of a liquid is set in rotation inthe direction shown by the arrow in Fig. 1, this surface is subject tothe laws of centrifugal force. It tends to emerge from the rotor wheel.The liquid which emerges must, however, be immediately replaced byliquid which follows it. However, in com sideration of the very enormousdifferences in the cross sectional area of the inlet 3 and the outlet 4of the blade passages it is not possible for the liquid to becomeaccelerated from the inlet to the blade to the outlet therefrom to suchpump.

3 an extent that the liquid which emerges can be immediately replaced.

The following deduction follows therefore from this consideration:

The surface E of the liquid is ejected from the wheel by centrifugalforce. Since the outlet 4 from the wheel is much too large in proportionto the inlet thereto, the liquid ejected cannot be completely replaced.Owing to this lack in the replacement, a moving away of the liquid fromthe concave side I2 of the blades occurs, i. e. a vacuum space R isformed which produces a considerably increased suctional action, so thatan ejector action, which is a function of the particular choice of thecross sectional area, is consequently formed. The liquid stream doesonly touch the back of the blades.

It will now be understandable that liquids which contain air for examplecan be delivered without difiiculty. The air is drawn off by the actionof the vacuum produced, without any very great adverse effect on thedelivery output.

The present invention realizes the ideal combination of the centrifugalpump rotor wheel with the action of the rotor wheel of a water ring airIn this way the penetration of the air into centrifugal pumps which hasbeen feared hitherto is no longer inconvenient.

Owing to the small number of rotor blades and also to the large crosssectional area that exists in the blade passages it is possible tomachine the surfaces of the blades and the inner surfaces of the wheelefiectively, thereby reducing the internal frictional resistance of therotor wheel and improving the degree of hydraulic efficiency of the pumprespectively.

The formation of a vacuum in the rotor wheel also prevents anycavitation effect therein.

Owing to the small surface tension due to the vacuum R, no vertexesoccur.

Owing to the suctional or ejector action produced in the rotor wheel itis no longer necessary to endeavour to obtain a positive blade coveringbut it is specially necessary, when dealing with substances whichcontain air, to make the blade covering negative by the angle a. Any airthat may have been carried in along with the liquid can only be expelledby centrifugal action by so doing.

Exhaustive experimental measurements have proved that in relation to thedegree of hydraulic efficiency of a normally constructed rotor wheel therotor wheel according to the invention is superior.

In Fig. 4 the lifting height in meters water col-' umn and theefficiency in per cent. are plotted against the delivery in liters/sec.The dotted lines belong to a low pressure rotor wheel of a well knownconstruction and the full line curves to a rotor wheel according to theinvention. The measurements were made under exactly identical conditionsin the same pump casing. The data of the rotor wheel according to theinvention used for these tests are:

Diameter of entry mm 150 Diameter of outlet mm 245 Number of blades 3Ball passage mm 54 and of the rotor wheel of ordinary construction:

Diameter of entry mm 150 Diameter of outlet mm 245 Number of blades 7Ball passage mm 17 The open rotor wheel shown in Fig. 5 has two blades5. With this wheel it is possible, when dealing with liquids whichcontainlarge quantities of air, to still further increase the effectobtained by the present invention. Owing to the open construction theaxial thrust of the pump is also very greatly reduced, so that in mostcases the provision of relief holes may be dispensed with. The action ofthe vacuum produced in the rotor wheel reduces the differences ofpressure very considerably.

The delivery in hitherto used pumps of liquids which contain air andthick substances failed because the occluded and adherent air separatedwhere the liquid or the thick substance entered the blades of the rotorwheel or at the outlet from the rotor wheel so that an air cushionformed in the pump casing, which reduced further conveyance if it didnot stop it altogether.

The present invention eliminates these disadvantages. The liquid or thethick substance is drawn in in a much better way by the increased vacuumwhich is produced in the rotor wheel. The conversion of the energy offlow into pressure energy takes place in great part already in the rotorwheel. No conversion of kinetic into pressure energy in a diffuserbecomes necessary, since the liquid leaves the rotor wheel with thepressure energy desired.

Hitherto, the delivery of frothing, saponaceous liquids or thicksubstances by means of centrifugal pumps ordinarily failed because thefoam was driven ofi on the entrance of the liquid into the rotor wheel,after which a plug of foam formed on the suction side which stopped anyfurther delivery by the pump.

The present invention enables the foam to be sucked within reach of theblades at a comparatively low speed, that is to say, to be drawn indirectly, and the air to be taken into the vacuum zone, while theliquid, almost free from air, flows along the back of the blades. Incases where an enormous quantity of foam is, produced it is alsopossible to allow the pump embodying the invention, to run light, thatis to say, the liquid entering it fills up only half the cross sectionalarea of entry of the suction branch, in which case an elfective removalof air from the pump on the suction side is produced. This case isillustrated in Fig. 6 which shows a pump 8 with a rotor wheel accordingto the present invention for liquids which froth strongly. As may beseen, a channel 6 supplies the material to the suction branch 1. Thismaterial only fills about half of the branch section. When a freelyfrothing liquid is to be delivered, the vacuum space (R in Fig. 1)collects the froth and an additional removal of air on the suction sidethrough the upper portion of the branch 1 sets in also. ContinuousWorking free from shock thereby results.

Thick substances of high concentration present special difficulties tothe conveyance thereof by means of centrifugal pumps. When highlyconcentrated the properties of the foreign substances, such for exampleas pulps, ground wood, potato pulp, spinach, tomato puree, and the like,replace the properties of the liquid almost entirely. Internal andexternal friction are increased considerably and the properties of theflow fall off in the same measure. In many cases a considerablepercentage of the volume is air. In consequence of this, these thicksubstances become more or less elastic liquids or pastes which havequite different properties of flow to those of water. Their behaviour innormal centrifugal pumps shows that owing to their sluggishness andtheir friction such thick substances can no longer be compared withwater.

If measurements with a pump of well-known type are made for waterdelivery, curve a in Fig. 4 is obtained for the lifting height plottedagainst the delivery. and the input may, for instance, amount to 5 H. P.

If measurements are made. with the same pumps for the delivery of thicksubstances, e. g. of paper pulp having a concentration of 6%, thelifting height is decreased to the curve d in Fig. 4 and the input isonly 2 H. P. This phenomenon may be explained as follows: The path x-xin Fig. l of a water particle from inlet to outlet shows that thisparticle must be accelerated to the velocity desired in-a relativelyshort time. A water particle may in this time indeed be accelerated tothe value desired. However, on delivery substances having propertiesquite different from water, tests have shown that the time available inpumps of known type is not sufficient, so that the input decreases veryconsiderably.

In the rotor wheel according to the invention the time conditions areconsiderably modified with regard to prior wheels. The substanceparticle has much more time to be accelerated and leaves the wheel atan. Measurements with a wheel according to the invention have shown thatthe curve for thick substances is now so much higher than the curve dthat the input is again H. P. Ideal conditions exist when the input forthe delivery of thick substances is the same as for water.

The present invention meets the demands of these special features. Byreason of its very large inlet cross sectional area and high vacuum therotor wheel is able to bring even viscous thick substances within reachof the blades of the pump. The position of the inlet edges of the bladesof the rotor wheel must correspond to the material which is to beconveyed. Once, however, the thick substance is in the blade passage itsdelivery is compulsory. The most important point in the delivery ofthick substances is the bringing of the material to be delivered intothe rotor wheel. Its further movement in the rotor wheel is then more aproblem of transport than a pump problem.

Liquids which contain fibrous, pasty and lumpy solid substances requirea formation of inlet and outlet edges and angles and also of thecorresponding cross sectional area of the blades passages of the rotorwheel such as to stop any choking. up or stoppage of the inlet, crosssectional areas.

The present invention meets these demands also. Strongly profiled inletedges of the blades without any dead corners and the one-sided admissionof the blades in the rotor wheel prevent fibres from adhering. Largecross sectional areas of inlet, produced by the small number of blades,allow even large foreign bodies to pass through. In consequence of thecomparatively low inlet and outlet velocities resulting from thecorresponding inlet and outlet cross sectional areas, lumpy solidsubstances can be conveyed without damage. In this case also it isnecessary to increase the suctional power of the pump considerably byincreasing the vacuum.

When the casing is of spiral shape the novel rotor wheel requires acasing tongue which is carried close up to the rotor wheel. The crosssectional areas of the casing must be kept as large as possible so as toobtain low speeds particularly when thick substances are being dealtwith.

Cal

An annular-casing with large cross sectional areas is, however, asadvantageous as a spiral casing.

The rotor wheel according to the invention can be mounted, eitherhorizontally or vertically, and the entrance of the material into thewheel can take place both radially or axially.

For the delivery of certain substances it is recommendable to provide acertain number (e. g.

three or four) of guide vanes 9 (Fig. 7) whichare fixed to the suctionbranch is ,and lie in front of the entrance 3 to the rotor wheel bladesH.

When the rotor wheel according to the present invention is used it isnot necessary to remove air from the casing of the pump previous tostarting, for this wheel provides for automatic suction.

The rotor wheel according to the invention may also be used for waterpumps: Owing to the small number of blades and the low velocities in therotor wheel, losses due to friction are reduced and the over-allefficiency of the pump thereby increased. The angles of entry and outletmust be selected in such a way they will ensure that the water, for alldeliveries, enters and leaves the rotor wheel with as little shock aspossible.

If the manometric pressure produced in one single rotor wheel is notsufilcient, the pump may be built as a multistage pump, a rotor wheelaccording to the invention being built into the first stage as a primingor feed-in wheel. The remainin stages may be of the type of const uctionwell known hitherto. In this way, the advanta es of the presentinvention are imparted to high pressure pumps.

What I claim is:

l. A rotor wheel for a centrifugal pump, comprising in combination, afirst ring-shaped impeller disc having an internal surface composed ofa. substantially cylindrical surface delimiting an inlet opening, of atoroidal surface extending outwardlv from said cylindrical surface andof a generally conical surface extending from said toroidal surface; asecond im eller disc coaxial with said first impe ler disc and being ofapproximate y the same outer diameter as the said first im eller disc,said second impeller disc having an internal surface formed by a surfaceof revolution located at a distance from the internal surface of thefirst impeller disc and pro ressing towards said inlet as the radius ofthe surface of revolution decreases, said distance decreasing graduallyfrom said inlet opening to approximately the transition of said toroidalsurface into said generally conical surface, and increasing fromapproximately this transition towards the periphery of the wheel; and arelatively small number of impeller vanes rigidly fixed to both of saidimpeller discs, said vanes being strongly curved towards the rear withregard to the direction of rotation of the wheel and arranged withregard to one another with a negative overlap, each of said vaneshavin'r an inlet edge which, in extending from said toroidal surface tosaid second impeller disc, approaches the wheel axis, and said vaneshaving outlet edges located in the proximity of the outer periphery ofsaid impeller discs.

2. The rotor wheel of claim 1, wherein each of said impeller vane isrounded at its inlet edge and becomes constantly thinner only outwardlyof a point located away from said inlet edges by a distance at leastequal to a third of the length of said vanes.

- 3. A centrifugal pump impeller comprising in combination, first andsecond impeller discs of approximately the same diameter coaxiallylocated in spaced relation with respect to each other, said discsrespectively having adjacent their peripheries opposite inner conicalsurface portions diverging in the direction of fluid flow through theimpeller, said first impeller disc being formed with a central,substantially cylindrical opening passing transversely therethrough andforming an inlet for the impeller, and said first impeller disc having acurved ring-shaped surface portion located between and merging into saidsubstantally cylindrical opening and said conical surface portion ofsaid first impeller disc, said second impeller disc having an innercurved ring-shaped surface portion located opposite said curved surfaceportion of said first impeller disc and merging into said conicalsurface portion of said secondimpeller disc, and said curved surfaceportions gradually converging in the direction of fluid flow through theimpeller up to the junction between said curved surface portion and saidconical surface portion of said first impeller disc; and negativelyoverlapping impeller vanes fixed between said first and second impellerdiscs, each of said vanes having an outlet edge adjacent the peripheriesof said impeller discs and an inlet edge extending from a first point onsaid curved surface portion of said first impeller disc to a point onsaid second impeller disc which is located nearer to the centers of saidimpeller discs than the edge of said inlet opening.

4. A centrifugal pump impeller comprising in combination two co-axialand spaced impeller discs having adjacent their peripheries oppositeconical diverging surface portions, one of said impeller discs beingformed with an axial entrance opening having an annular surface portionand with a curved surface portion merging along one edge into saidannular surface portion and along its other edge into the conicalsurface portion of said one impeller disc, and the other of saidimpeller discs having in addition to its conical surface portion aninner curved surface portion merging into the conical surface portion ofsaid other impeller disc, located .opposite said curved surface portionof said one impeller disc, and projecting into said annular entranceopening of the same; and a plurality of impeller vanes having a negativeoverlap and secured at opposite edges to said impeller discs, each ofsaid vanes having an inner inlet edge extending between said curvedsurface portions of said impeller discs and an outer outlet edgeextending between corresponding points of the peripheries of saidimpeller discs.

5. A centrifugal pump impeller arrangement comprising, in combination,first and second coaxial spaced discs having adjacent their periphcriesopposite conical diverging surface portions, said first disc beingformed with an axial entrance opening having an annular surface portionand with a curved ring-shaped surface portion merging along one edgeinto said annular surface portion and along its other edge into theconical 8 surface portion of said first disc, and said second dischaving in addition to its conical surface portion an inner curvedring-shaped surface portion mergin into the conical surface portion ofsaid second disc, located opposite said curved ring-shaped surfaceportion of said first disc, and projecting into said annular entranceopening of the same; and a plurality of impeller vanes having a negativeoverlap and being fixedly connected to at least one of said discs, eachof said vanes haying an inner inlet edge extending between said curvedring-shaped surface portions of said discs and an outer outlet edgeextending between corresponding points on the peripheries of said discs.

6. A centrifugal pump impeller arrangement, comprising in combination,first and second discs of approximately the same diameter coaxiallylocated in spaced relation with respect to each other, said discsrespectively having adjacent their peripheries opposite inner conicalsurface portions diverging in the direction of fluid flow through theimpeller, said first disc being formed with a central substantiallycylindrical opening passing transversely therethrough and forming aninlet for the impeller arrangement, and said first disc having a curvedring-shaped surface portion located between and merging into saidsubstantially cylindrical opening and said conical surface portion ofsaid first disc, said second disc having an inner curved ringshapedsurface portion located opposite said curved surface portion of saidfirst disc and merging into said conical surface portion of said seconddisc, and said curved surface portions gradually converging in thedirection of fluid fiow through the impeller arrangement up to thejunction between said curved surface portion and said conical surfaceportion of said first disc; and negatively overlapping impeller vanesfixedly connected to at least one of said discs, each of said vaneshaving an outlet edge adjacent to the peripheries of said discs and aninlet edge extending from a first point on said curved surface portionof said first disc to a point on said second disc which is locatednearer to the centers of said discs than the edge of said inlet opening.

EGGER, EMILE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 21,756 Hibbard Oct. 12, 1858678,223 Christian July 9, 1901 867,069 Neumann Sept. 24, 1907 1,050,698Scheurmann Jan. 14, 1913 1,909,052 Froisland May 16, 1933 2,074,650Holdaway Mar. 23, 1937 2,420,420 Durdin, Jr May 13, 1947 FOREIGN PATENTSNumber Country Date 65,687 Austria 1913 82,191 Austria 1920 537,282Great Britain 1941

